1. Field of the Invention
The present invention relates to a throw-away tipped drill, to which a throw-away tip of an approximately flat plate shape and formed with a sharp cutting edge (hereinafter sometimes also termed simply a “tip”) is fitted in a detachable and attachable manner at a tip attachment seat thereof which is made as a concave groove formed in an end portion of the drill main body; and the present invention also relates to such a throw-away tip, and to such a drill main body.
Priority is claimed on Japanese Patent Applications No. 2003-58473, filed Mar. 5, 2003, No. 2003-83044, filed Mar. 25, 2003, No. 2003-419408, filed Dec. 17, 2003, No. 2004-11826, filed Jan. 20, 2004, and No. 2004-11827, filed Jan. 20, 2004, the contents of the applications are incorporated herein by reference by their entirety.
2. Description of Related Art
One example of such a type of throw-away drill is shown in, for example, Japanese Patent Application, First Publication No. Hei 11-197923. With this drill, a round hole is formed in the bottom surface of a concave groove shaped tip attachment seat which opens at an end surface of the drill main body, and a shaft portion which can be fitted into the above described round hole is provided at an after end surface of an approximately flat plate shaped tip which is fitted to this tip attachment seat. The tip is fitted to the tip attachment seat by the shaft portion being inserted into the round hole, so that an engagement member which projects from the inner periphery of the round hole engages with a cutaway portion which is formed upon the shaft portion.
With this throw-away tipped drill, since the fitting of the tip can be performed just by inserting the shaft portion of the tip into the round hole in the tip attachment seat, accordingly it possesses the beneficial feature that it is easy to perform the task of changing the tip. However, since the connection between the tip and the drill main body is only performed via the shaft portion, there has been a possibility that the accuracy of position determination (centering) of the tip with respect to the drill main body can be insufficient, which can exert a negative influence upon the accuracy with which a workpiece can be processed using the drill.
In this connection, in a patent application which is assigned to the same assignee as the present application, there has previously been proposed a throw-away tipped drill as shown in FIGS. 15 and 16. With this throw-away tipped drill, a pair of chip disposal grooves 2 are formed on the outer periphery of a drill main body 1 which rotates around an axial line O, and, at an end portion of the drill main body 1, there is formed a concave groove shaped tip attachment seat 4 which, along with communicating to these chip disposal grooves 2, also opens to the end surface 3 of the drill main body 1.
On the tip attachment seat 4, there is formed a tip 5 of approximately flat plate shape with a cutting edge formed upon its edge, and a pair of outer side surfaces 5A of said tip 5 are opposed to a pair of internal side surfaces 4A of the tip attachment seat 4; and, moreover, raked surfaces 5B are inlaid into the outer side surfaces 5A of this tip 5, being formed at portions which face forward along the rotational direction T of the drill, in a state of opening to the chip disposal grooves 2. Further, the tip 5 is clampingly supported by the tip attachment seat by the pair of internal side surfaces 4A of the tip attachment seat 4 being mutually squeezed together by the use of a clamp bolt 8 (in FIG. 15, only the axial line L of this clamp bolt 8 is shown) which is screwed into the end portion of the drill main body 1 so as to cross across the tip attachment seat 4.
Guide grooves 6 which extend along the axial line O are formed upon portions of the internal side surfaces 4A of the tip attachment seat 4 which face forwards in the rotational direction T of the drill. Furthermore, convex portions 7 which can be engaged with the above guide grooves 6 are formed upon portions of the outer side surfaces 5A of the tip 5 which face rearwards in the rotational direction T of the drill, and the accuracy by which the tip 5 is maintained in position with respect to the drill main body 1 is enhanced by the mutual engagement of these guide grooves 6 and these convex portions 7 with one another.
As shown in FIG. 16, the clamp bolt 8 is screwed into a through hole 9 which is provided as crossing across the tip attachment seat 4 in an end portion of the drill main body 1 when viewed in a perpendicular cross section to the axial line of the drill main body 1. This through hole 9 is formed so as to extend along the diametrical direction of the drill main body 1, through both a one (a first end portion 1A) and another (a second end portion 1B) of two end portions 1A and 1B, into which the end portion of the drill main body 1 is divided by the tip attachment seat 4; and its opening end, along with opening to the outer peripheral surface of the first end portion 1A of the drill main body 1A, is made as a concave portion 9A which houses the head portion 8A of the clamp bolt 9 which is inserted into the through hole 9, while its portion which is positioned within the second end portion 1B is made as a threaded portion 9B, into which a threaded portion which is formed upon the side surface of the shaft portion 8B of the clamp bolt 8 which is inserted into the through hole 9 is screwingly engaged.
In this drill, by inserting the clamp bolt 8 into the through hole 9, and by screwingly engaging together the threaded portion which is formed upon its shaft portion 8B and the threaded portion 9B which is formed in the through hole 9, the first end portion 1A and the second end portion 1B are elastically deformed so as to mutually contact against the pair of internal side surfaces 4A of the tip attachment seat 4. As a result, the pair of outer side surface 5A of the tip 5 are pressed against the pair of internal side surfaces 4A of the tip attachment seat 4, whereby the tip 5 is clamped and supported by the tip attachment seat 4. Since in this manner the tip 5 is supported by the tip attachment seat from its rear end (the rear end side of the drill main body 1) and from the rearward side of the rotational direction T of the drill, thereby, when performing the processing of a workpiece by drilling a hole therein, the tip 5 is held by the tip attachment seat 4 so as to be pressed thereagainst and fixed thereto.
However, when using a clamp bolt 8 of the above described type for holding the tip 5, the first end portion 1A of the drill main body 1 is elastically deformed so as to be deflected inwards by the concave portion 9A of the through hole 9 which is formed in said first end portion 1A being pressed by the head portion 8A of the clamp bolt 8. In contrast, the second end portion 1B of the drill main body 1 is only elastically deformed by being stretched inwards by the shaft portion 8B of the clamp bolt 8 being threadingly engaged with the threaded portion 9B of the through hole 9 which is formed in the second end portion 1B. Due to this, the pressing forces which are applied when the pair of internal side surfaces 4A of the tip attachment seat 4 press against the respective ones of the pair of outer side surfaces 5A of the tip 5 come to be mutually unequal, which is undesirable.
In other words, since the first end portion 1A which is elastically deformed by the head portion 8A of the clamp bolt 8 so as to be pressed inwards is deformed to a greater amount than is the second end portion 1B which is elastically deformed so as to be pulled inwards by the screwing in of the shaft portion 8B of the clamp bolt 8, thereby the force by which the internal side surface 4A of the tip attachment seat 4 which is positioned on the side of the first end portion 1A, the flexing amount of which is the greater, is pressed against its outer side surface 5A of the tip 5, comes to be greater than the force by which the other internal side surface 4A of the tip attachment seat 4 which is positioned on the side of the other second end portion 1B, the flexing amount of which is the lesser, is pressed against its outer side surface 5A of the tip 5. Due to this, the problem arises that the tip 5 comes to be held by a squeezing force whose strength is inadequate, and the accuracy of deflection of the cutting edge of the tip 5 is deteriorated.
Furthermore, with the above described throw-away tipped drill, although the shifting of the tip 5 which is fitted to the drill main body 1 towards its end is restricted, this is only performed by the frictional force which is generated between the pair of internal side surfaces 4A of the tip attachment seat 4 and the pair of outer side surfaces 5A of the tip 5 due to the clamp bolt 8 being tightened up. Because of this, when for example performing the processing of a workpiece by drilling a deep hole therein, if the hole should become angled or the like, the load which is imposed upon the drill main body 1 becomes great, and, if the space between the first end portion 1A and the second end portion 1B should widen, which is undesirable, then the clamping force for the tip 5 will be deteriorated, and, if the tip 5 should catch against the inner surface of the hole when the throw-away tipped drill is being pulled out from the workpiece, or the like, then it may happen that the tip 5 comes away from the drill main body 1, which is extremely undesirable.
Yet further, with the above described throw-away tipped drill, the pair of raked surfaces 5B which are provided to the tip 5 which is fitted to the tip attachment seat 4 are in a state of opening towards the respective ones of the pair of chip disposal grooves 2. Due to this, when the pair of outer side surfaces 5A of the tip 5 are pressed by the pair of internal side surfaces 4A of the tip attachment seat 4 being mutually brought together by the clamp bolt 8, and thereby the tip 5 is fixedly fitted to the tip attachment seat 4, inevitably the tip 5 is deformed towards the forward rotational direction T (as shown in FIG. 15 by the white arrow signs), which is very undesirable.
Accordingly, it becomes difficult to keep the portions upon the pair of outer side surfaces 5A of the tip 5 which face towards the rearward direction of the rotational direction T of the drill firmly pressed against the pair of internal side surfaces 4A of the tip attachment seat 4, and, as a result, it either simply becomes difficult to hold the tip 5 as strongly fixed in the tip attachment seat 4, or, even if a construction such as the one described above is employed in which the convex portions 7 and the guide grooves 6 are mutually engaged together, the accuracy of positional determination of the tip 5 with respect to the drill main body 1 becomes insufficient.
The present invention has been conceived of in the light of the above described problems, and its primary objective is to provide a throw-away tipped drill in which it is ensured that the pressing force when pressing the pair of outer side surfaces of the tip with the pair of internal side surfaces of the tip attachment seat using the clamp bolt are mutually equal to one another. Furthermore, another objective of the present invention is to provide a throw-away tipped drill, and a tip and a drill main body which are utilized therein, in which coming away of the tip from the drill main body is reliably prevented. Yet another objective of the present invention is to provide a throw-away tipped drill with which it is possible to fit a tip to a concave groove shaped tip attachment seat which opens at an end surface of the drill main body with a clamp bolt in a strong manner. Still another objective of the present invention is to provide a throw-away tipped drill, and a tip and a drill main body which are utilized therein, with which it is possible to prevent the tip from coming away from the drill main body.